The present invention relates to a magnetic disk apparatus and a head-supporting mechanism for the magnetic disk apparatus and, more particularly, to an actuator for high-accuracy positioning of a head that performs the writing-in and reading-out of information in a predetermined position on a magnetic disk on which information is stored.
A voice coil motor has so far been used as an actuator for moving a magnetic head over a desired position on a disk. However, this method had its limits when positioning accuracy was to be improved.
Therefore, in order to ensure that a magnetic head performs higher-accuracy positioning, arrangements in which a second actuator for the fine adjustment of the magnetic head position is disposed between the voice coil motor and the magnetic head have been proposed.
For example, the construction of a second actuator described in JP-A-12-113615 is such that in a magnetic disk apparatus comprising a magnetic head that performs the writing-in and reading-out of information, a magnetic disk on which information is stored, an elastic member which supports the above head, a fixed member which supports the above elastic member, a first actuator for rough movement which moves the above magnetic head over a predetermined position on the magnetic disk, and a second actuator for fine movement which is disposed between the above first actuator and the above magnetic head, the second actuator is a sheet-like structure formed from one piezoelectric flat sheet having electrodes on the top and bottom surfaces and two or more polarized regions in the interior or a plurality of such laminated piezoelectric flat sheets, and the second actuator, which is the above sheet-like structure, is disposed so that the top surface or bottom surface of the second actuator bridges the top surfaces of the above fixed member and above elastic member or the bottom surfaces of the above two members.
Furthermore, the above second actuator is a sheet-like structure made of a piezoelectric material and comprises one piezoelectric flat sheet having electrodes on the top and bottom surfaces or a plurality of such laminated piezoelectric flat sheets. At least one of the above electrodes on the above top and bottom surfaces is separated into two or more portions. The above piezoelectric flat sheet has in the interior a non-polarized region and two or more polarized regions separated by part of the above non-polarized region and polarized in the direction of thickness of the above piezoelectric flat sheet. The above piezoelectric flat sheet is displaced in its in-plane direction by applying an electric field to the above two or more polarized regions within the above piezoelectric flat sheet in the thickness direction of the above piezoelectric flat sheet by using the above electrodes on the top and bottom surfaces of the above piezoelectric flat sheet.
Because the second actuator in the above prior art is made of ceramics comprising PZT (lead zirconate titanate), etc. which provide a piezoelectric element, the actuator itself is mechanically brittle and mechanical strength poses a problem. Furthermore, this actuator must be metallized with Au, etc. so that electrodes are attached thereto. Therefore, when the element is caused to expand and contract by applying a voltage, fine particles of PZT and Au are generated as dust. These dust particles adhere to the magnetic head and disk, not only contaminating the interior of the magnetic disk apparatus, but also causing a decrease in reliability during the writing-in and reading-out of information.
The object of the present invention is to solve the above-mentioned problem and realize in providing a magnetic disk drive apparatus having a high reliability.
In order to solve the above problem, we carried out experiments and examinations and, as a result, it became apparent that this problem can be solved by the following method.
We found that in a magnetic disk apparatus having a second actuator comprising a piezoelectric element, by the resin coating of the surface of the second actuator, i.e., by applying a liquid adhesive to the surface of the second actuator and causing the adhesive to set, it is possible to prevent fine particles of PZT, which is a material of the actuator, and those of the Au with which the surface is metallized, from being generated as dust during the expansion and contraction of the element while a voltage is being applied.
Details of this method will be described below.
The liquid adhesive used in resin coating is uniformly applied with a film thickness of not more than 10 xcexcm by usual means such as a dispenser and ink jet and, therefore, it is desirable to use a low-viscosity resin that has a viscosity before curing of not more than 1000 mPaxc2x7s.
Photo-setting (UV and visible light) type resins may be used as the resin for application use. However, when thermosetting resins are used, they should be a type that sets at a temperature not higher than the temperature which the piezoelectric element can withstand. Furthermore, resins which combine thermocuring and photo-setting properties may be used in the case of the type which cures at a temperature not higher than the temperature which the piezoelectric element can withstand.
If volatile organic molecules are generated as an outgas from a resin after setting, these volatile organic molecules adhere to the magnetic head and disk, not only contaminating the interior of the magnetic disk apparatus, but also causing a decrease in reliability during the writing-in and reading-out of information. Therefore, the resin for application use must be an adhesive that produces little outgas of, resin after setting.
Moreover, as the properties required of the resin, the adhesive must have a high adhesive strength relative to the Au used in metallization and flexibility after curing so that cracks, etc., are not formed during the expansion and contraction of the piezoelectric element to which a voltage is applied, and at the same time the adhesive must have a low elastic modulus, a high elongation and a low hardness value.
We earnestly examined resins that have these required properties and, as a result, we found that a low-viscosity epoxy resin-based adhesive is an optimum one.
This low-viscosity epoxy resin-based adhesive comprises epoxy oligomer of less than 20 wt % and epoxy monomer of not less than 80% and further contains a polymerization initiator which reacts with heat and light, a catalyst and an additive.
The polymerization initiator that reacts to heat and light and the catalyst may be any of amine-based, acid anhydride-based and cation-based ones.
The additive can be added as far as it does not have an adverse effect on the adhesive property and other properties of the resin. The additive is a surfactant for improving the wettability of an adherend sursurface, a filler for improving the physical properties of a set substance, etc.
For example, Worldlock XOC-11CKF-3 and XOC-11CKF-3H made by Kyoritsu Kagaku Sangyou, etc., can be enumerated as such low-viscosity epoxy resin-based adhesives. However, it should be understood that low-viscosity epoxy resin-based adhesives are not limited to them. Such low-viscosity epoxy resin-based adhesives may be appropriately prepared from epoxy oligomer of less than 20 wt % and epoxy monomer of not less than 80 wt % and further a polymerization initiator with with heat and light, a catalyst and an additive.
On the other hand, adhesives other than low-viscosity epoxy resin-based adhesives are unsuitable as the resin of the invention.
For example, general low-viscosity coating agents are undesirable because they contain solvents or are acrylic resins and, therefore, a large amount of outgas is generated from theses resins after setting.
Because general epoxy resins contain a large amount of epoxy oligomer and have high viscosity, it is difficult to uniformly apply such resins with a film thickness of not more than 10 xcexcm. Furthermore, because these resins after curing lack flexibility and are hard, cracks, etc., are formed by the expansion and contraction of the piezoelectric element during voltage application, causing dust generation, if these resins are used in the actuator. Thus general epoxy resins are also undesirable.